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It really depends on the type of shock but say anaphylaxis causes blood vessels to dilate, resulting in lower blood pressure. A lower blood pressure will eventually lead to not enough blood reaching vital organs in time which is bad for you.
Shock is a medical term used to describe any hindrance of regular blood flow. It's not the same as being 'shocked', like if something traumatic happened to you.
OK so it's like the blood is going more slowly? So does shock only happen when someone has a problem with their blood?
Not slowly per se. More like not enough to go around. Heart rates spike when blood pressure drops to try to move the lower volume around faster, but even that emergency autonomic response can lead to other problems.
Does it only happen with problems with blood (like bleeding): no. Other responses to trauma, both physical and mental, can lead to a person's body pushing blood to the surface muscles, which can deprive the vital things like organs and brains of sufficient blood. In normal cases this is just fight or flight systems kicking on. More blood to muscles is good there. But it can go too far and lead to these problems. Bodies overcorrect all the time - think dangerous fevers, or dangerous allergic reactions.
Could we say that the shock moment is the moment vital organs get damage cause not enough nutrients reach them?
No, a state of shock causes less blood going to vital organs. You can be in shock for a short while without sustaining any heavy damage.
Shock mainly constricts blood vessels.
Fwiw, there's more than one kind of shock, and they're handled differently.
Hypovolemic shock is the one that makes the least sense if you don't have a background that includes medical terminology. Hypovolemic just means a low amount of blood. That's when you get stabbed and bleed out, as ine example. But it can also occur via severe dehydration as the volume of blood also decreases then.
You've got obstructive, where something is in the way of your blood circulating properly, usually due to something like excess pressure around the heart, preventing it from doing its job correctly. Think chest injuries where blood pools around the heart preventing it from being able to contract and expand properly as an example.
In all of those cases, you end up with organs not receiving the supplies they need to function, which leads to cell death. As enough cells die, organ function decreases. As that happens, you start seeing a cascade where one failure accelerates the rest. At some point, it becomes too much and the heart and/or brain start dying. At that point, there's pretty much no recovery, particularly with the brain since even the really improbable events that might allow a person to survive all the other organs failing if it was slow enough don't apply to the brain. You can't hook up a brain to a machine that will duplicate its function. So even if you manage to keep the rest of the body "alive", the person is dead.
And that's a good segue into the cardiogenic type of shock. Again, the word itself just means that the problem originates (genic) from the heart itself (cardio). The classic example is a heart attack. A clot or other blockage inside the heart makes the heart less able or unable to pump.
Then you get into distributive, where the vessels throughout the body are in a condition where the volume of blood can't sustain function. That's where allergies come in, as well as sepsis or neurological (usually brain, but can be due to other nerve issues). Basically, the vessels all open up wider, so the volume of blood you have isn't high enough to sustain pressure and therefore proper blood flow and oxygenation.
Tbh, I've always had a pet peeve about the term shock. The etymology of that usage makes sense, but it's confusing without knowing the etymology. It goes back to translation choices. A few hundred years ago, someone was translating from French to English, and chose shock as the closest in meaning.
Which it is a good word for what was being described: the sudden and intense loss of blood alongside other factors after a gunshot. That's the "shock" it came from: a specific sudden, unexpected event.
But not all "shock" is sudden or unexpected in the medical sense, so people don't think of it when the symptoms are otherwise right there and in need of quick action, which is particularly true of sepsis. The way sepsis often ends up lethal is delayed treatment. You catch it early, and there's options. You wait until the person is in a condition that most people will call an ambulance, and probabilities of survival shift.
I mean, the delay in treatment is a factor in shock deaths across the board, but more people recognise how emergent a heart attack or anaphylaxis are, so they'll likely react sooner than with "just" feeling sick.
Touching exposed cables.
Shock-induced cardiac arrest?